This project seeks to improve the radioisotopic methods for the diagnosis of renal disease suitable for screening large groups of patients. An animal model has been developed for the assessment of renal radioisotopic agents, in which the renal microvasculature of one kidney is selectively and quantitatively reduced by the injection of a known quantity of 35 micron carbonized microspheres through a renal artery catheter. Subsequently, various radioactive agents are administered by successive intravenous injections, and their renal accumulation measured by a scintillation camera and dedicated digital computer. The efficacy of established radiopharmaceuticals, including I131-orthoiodohippurate, 99mTc-ferrous-ascorbate complex, and Hg197-chlormerodrin is being compared. New radiopharmaceuticals which exhibit renal localization and which can be labeled with gamma emitters such as 99mTc are being formulated, and compared with older radiopharmaceuticals for diagnostic efficacy in this animal system. The scintillation camera-computer techniques and newer radiopharmaceuticals will be used for the diagnosis of renal disease in selected series of patients.